1. Technical Field
The present invention relates to a method of controlling a recording head that records information by driving recording wires to form dots on recording paper, and to a dot impact printer having the recording head. More particularly, the invention relates to a method of controlling a recording head that can suppress a drop in print throughput while preventing heat damage to the head coil resulting from heat produced while printing, and to a dot impact printer.
The invention claims priority based on Japan patent application 2009-294060 filed Dec. 25, 2009, Japan patent application 2010-133686 filed Jun. 11, 2010, and Japan patent application 2010-133687 filed Jun. 11, 2010, the contents of which are incorporated herein by reference.
2. Related Art
Dot impact printers are used in various fields for the primary purposes of high reliability and overstrike printing on multipart forms. Dot impact printers use a recording head with plural recording wires (wire pins). For each recording wire, the recording head has an electromagnetic coil (head coil) that drives the recording wire, and the recording wires are selectively driven to protrude and form a dot by selectively driving the electromagnetic coils. Dot impact printers have a carriage that carries the recording head, and record information by selectively causing the recording wires of the recording head to strike the recording paper with an ink ribbon therebetween while moving the carriage back and forth widthwise to the recording paper.
When the recording wires of a dot impact printer are driven continuously or at a high frequency, the temperature of the head coils (electromagnetic coils) that are driving those recording wires rises quickly. In extreme cases, the coils may burn out. Therefore, to prevent such problems as the head coils burning out, the temperature of the recording head is detected by a thermistor or other temperature detector so that the heat output of the head coils can be reduced when the temperature rises to a level where there is a danger of heat damage. For example, when the temperature of the recording head reaches a preset slowdown temperature setting, the drive frequency of the head coil is reduced and the printing speed is reduced. When the temperature of the recording head reaches a preset stop-temperature setting, the printing operation of the recording head is stopped. Dot impact printers that thus control operation so that the head coils do not reach a burnout threshold temperature are thus known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2003-127441.
However, when the head coil temperature rises suddenly, there are situations in which the head coil may exceed the burnout threshold temperature before the temperature detector detects that the head coil has reached the preset temperature and action to reduce the print speed or stop printing can be taken, and the coil cannot be prevented from burning out. To prevent such problems, the dot impact printer described above presets specific dot patterns (specific recording patterns) that can be expected to produce a sudden temperature rise. When a specific recording pattern is detected during printing, the printing is controlled with the slowdown temperature setting and stop-temperature setting set lower than normal. As a result, when the head coil temperature rises rapidly, the printing speed can be lowered or printing stopped before the head coil reaches the burnout threshold temperature.
This dot impact printer changes the slowdown temperature setting and stop-temperature setting to a low temperature even when the specific recording pattern is detected in only one place. As a result, the print speed is reduced or printing is stopped even if the recording head temperature is low enough when the specific recording pattern is printed that the burnout threshold temperature would not be reached by printing the specific recording pattern. More specifically, the dot impact printer described above may reduce the print speed or stop printing even when reducing the print speed or stopping printing is not necessary, and printer throughput therefore drops.